1. Field of Invention
The present invention relates generally to joining two surfaces together using brazing, and more particularly, to an improved braze join.
2. Related Art
Active medical implants are used in many applications in medicine, and include implants for components of the heart, regulated drug delivery systems and cochlear implants. It is essential that these implants are hermetically sealed to prevent the ingress of bodily fluids to the interior of the device as well as contamination of the body from components within the device.
One aspect of hermetic enclosures for active medical implants is electrical connectivity from inside to outside the enclosure, such as connection of the electrical electrode array of a cochlear implant to the electronic circuitry within the hermetic enclosure. A typical construction for this is shown in FIG. 1. Typically, multiple conductive elements 11 are fabricated into a ceramic block to form a feedthrough 10. This may be achieved using processes as described in U.S. Pat. No. 5,046,242 or International Patent Application published as WO2004/030159, which are hereby incorporated by reference herein.
As shown in FIG. 2A, the feedthrough 10 component is then brazed using a braze alloy 12 such as TiCuNi to another component, such as a flange 20. Flange 20 can then be joined (e.g. by laser welding) to the rest of the enclosure (not shown) which is typically formed from a biocompatible metal such as titanium.
FIG. 2B shows a cross section along the line A-A in FIG. 2A, showing flange 20 connected to feedthrough 10 via braze alloy 12.
In practice, a solid ring of braze material or alloy is placed in the gap between feedthrough 10 and flange 20. Brazing is then achieved by heating the assembly to above the melting temperature of the braze alloy but below the melting point of the metal enclosure or ceramic.
One problem, which is common during the typical brazing process, is braze alloy flowing across the surface of the ceramic feedthrough 10 and inadvertently contacting the conducting elements 11. This is typically known as “flooding”. Because the braze material 12 is electrically conductive, this braze flooding 13 can cause short circuits between the conductive elements 11 (see FIG. 3) and the resulting assembly has to be discarded.